Quoted from ramegoom:
With regard to bumping the outlane rails: I would advise against it. The playfield is roughly 1/2" thick, and the rails are set the entire depth of the thickness. You will need at least a good 1/4 inch rise over factory location. But. By bumping them even 1/4 inch, you are weakening the hold on the rail and if hit hard enough, run the chance of chipping or damaging the playfield at the drilled hole. Then you're in trouble.
Just my opinion.
Of all the B/W games I've owned and restored, none had lane guides that run all the way through the PF. With as sung as those guides fit into the holes, I wouldn't have any worries whatsoever about this. 1/4" to 3/8" deep is plenty to secure it into the pf in my experience.